Antenna systems come in a variety of forms. Of particular popularity now are systems built on Printed Circuit Boards (PCBs). For example, a PCB patch antenna includes a radiating portion that is disposed on a layer of a PCB and a ground plane that is disposed on another layer either above or below the radiating portion (where “above” and “below” refer to positions in the stack of layers). Since the radiating portion of a patch antenna utilizes the ground plane, it is called a grounded antenna. Other antenna elements are not oriented above or below a ground plane and are referred to as ungrounded antennas. A Planar Inverted F Antenna (PIFA) can be made from some patch antennas by shorting an end of a patch element to ground. Many antenna elements are associated with parasitic elements to change a pattern and/or add frequency bands to the antenna's operational spectrum.
One example of a use of an antenna system is IN a direction finding (or beacon finding) antenna system. A current use of direction finding antenna systems includes finding sources of Radio Frequency (RF) interference (sometimes called “electromagnetic interference” or “EMI”) or finding beacons.
The prior art includes some designs for indicating a direction of a Radio Frequency (RF) beacon. Prior art direction-finding antennas use one of two technologies. The first technology is a highly directive antenna beam, such as that produced by a Yagi antenna or a phased array. A highly directive antenna beam can sometimes give a good indication about the direction of an RF beacon. Generally, when the beam is swept across all azimuthal directions, the direction with the greatest signal strength is a likely candidate for the direction of the beacon. Highly directive antenna systems, however, are often large and unwieldy, thereby causing them to be unfit for portable or casual use.
The other technology that is employed in current direction finding antenna systems includes calculating a signal strength difference in two antenna beams. One antenna beam is substantially uniform in all azimuthal directions, whereas the other antenna beam includes a plurality of nulls. An example prior art system includes a dipole and a slot antenna placed on a PCB. When a beacon is along an azimuth with a null, the signal strength difference between the uniform beam and the beam with the null is large, thereby giving an indication of direction. However, multiple nulls means that there is more than one azimuthal direction that shows a large signal strength difference. In the case of dipole/slot systems, the nulls are 180 degrees apart, so that a large signal strength difference either means a user is directed in the right direction or exactly in the wrong direction. Currently there is no direction finding antenna system on the market that is compact and provides for unequivocal indications of azimuthal direction of a transmitter.